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Natural and Industrially-produced materials require some form of surface modifications or treatments, before being put to functional use, or for readying them for the next process. Surface modification at a basic stage, consist of cleaning and mechanical scrubbing. The surface modifications are for creating use-worthiness by levelling, texturizing, or for application of additional materials for shielding. The surface modification starts with visual observation and touch-feel experience that no foreign materials have remained on the surface, and all loose (removable) materials are removed. These simple processes ensure integrity of the surface.

At another level Surfaces Modifications are not attempted, but such situations are negotiated with technologies. These include defining means to override the hindrances of texture, handling issues, electrical and other properties. These technologies also include forming shields around the users, tools and other equipments rather then over objects. The shields are physical layers and non-physical arrangements like restricting the exposure through time-space management.

In early ages, the surface modification and applications were an integrated process for exploiting the surface of any object. Primitive arts and crafts had a comprehensive treatment that consisted of 1: Modification of the surface, 2: Application of surface forming materials, and 3: Rendering new textures and tonal variations or shades. At a later stage an additional treatments for protection of the new surface were devised.

The Physical processes are mainly used to remove unwanted particles or materials (such as rust, nodules, residual deposits, dust or grease, lubricants, cutting-oils, etc.) adhering to the surface. Rubbing, air-dusting, vacuum cleaning, wiping, water-bathing, etc. remove such adhered materials. The particles have remained on the surface due to the holding by surface texture, bonding or ion attraction, and horizontal storage. Washing with soap or a surface active agent (surfactant) can weaken the ion attraction break the weak molecular bond generate by-products that can be removed easily.

The Chemical processes include acid-alkali treatments and solvent washing. The processes roughen, etch or smoothen the surface. In many instances the resultant by-product is beneficial or neutral, and so allowed to remain on the surface. In other instances a secondary treatment is required just to remove the by-products of the first treatment. Sometimes Surface preparation agents themselves are the primary surface finishes. Such agents cover the surface area as an intermediary film. Such films help in bonding of the final surface finish. Chemical processes also include burnishing, flame-treatments, surface annealing and hardening, cathodic modification, sputtering and material’s depositions.

Surface levelling is achieved by scrubbing or rubbing off the impurities, removing select protruding sections, or by skinning the entire surface area. In later cases there are chances of removing a seasoned or matured face and exposing a fresh one. Partial scrapping of the surface creates qualitatively unequal zones. This is the reason why over the ages levelling ‘plasters’ have been preferred. The ‘plasters’ can be thin coating, or an application of thicker mass. These were often rendered with patterns and textures or ‘loaded’ with minerals and colourants. Wet surfaces were, either, engraved or embossed with patterns to encourage the penetration of colours, to produce a bas or relief effect, or provide a highlighting boundary to the drawn object. Colours were blown as dry powders or applied as pastes and dabbed (pressed) into the wet plaster.

Gesso, a mixture of plaster of Paris (or gypsum) with size, is the traditional ground. The first layer is of gesso -grosso, a mixture of coarse, un-slaked plaster and size. This provides a rough, absorbent surface for ten or more thin coats of gesso sotile, a smooth mixture of size and fine plaster previously slaked in water to retard drying. This labourious preparation, however, results in an opaque, brilliant white, light-reflecting surface, similar in texture to hard, flat icing sugar.

Glass has been used in architecture in THREE major ways. It has been used as a space moulding surface material, environment controller and for the metaphysical allusions.

Central Library Seattle Washington

Architecture has always been manifestation of surfaces. The surfaces have been predominantly opaque and omnipresent. This aspect has been sought to be dissolved in many different manners. The textural character of the built mass with its varying shadows has enlivened the surface. Structures like the pyramids or the burial chambers of Newgrange were monotonous, because the texturing elements were too small for the extent of the surface. The surfaces of later structures were further surface- modulated with incised with figures, writings or colour variations of materials. Large variegation of gaps, openings and massive impositions of columns and projections further dissolved the monolithic character of the form.

Chichen Itza pyramid Mexico

The diffusion of outer skin of a building was not desirable. In Egyptian or the Indian temples it exposed the inner areas to weather. The surface conversions for texturizing must remain an overt change, and for that reason an envelope was required. The envelope in Parthenon and other buildings were exterior surface composition. The inner core, covered by the outer skin had little need for surface treatment.

Erechtheion of the Acropolis, Athens

The monolithic nature of building and its surface character began to change with additions of functional units, such as wings, blocks, towers, campaniles and ambulatory spaces. The openings were made emphatic with various architectonic elements.

St. Michael’s Church, Hildesheim Architectural elements moulding the form

The building’s exterior surface was fairly complex arrangement of forms. The interior surfaces though remained moderately plain, devoid of any play of architectural features. Interior surfaces of the Santa Sophia, Constantinople, were masked with bends of various materials, tying up openings, columns, etc.

The Glass was not yet a force as a space moulding surface material. Its size was small, life short, quality inferior and very costly. It was just an illumination element that allowed, light without rains, winds minus the cold or warmth. It replaced parchment, alabaster, etc. The walls were massive to allow large sized openings. The framing techniques with stone, wood, and lead caulking were poor.

By Romanesque period there was realization that Glass is a good controller of environment. It could simultaneously protect and illuminate the interiors. Other realization was that, glassed openings shone at night, giving a brilliant recognition to the architecture. The same glass during day time, in spite of colour staining had lusterless or dull metallic grey face.

Strasbourg Cathedral, France The glass face during day time from outside was dull metallic grey surface

The interiors of the buildings of religious order were mural painted, but for that to be seen day time illumination was required. The openings seemed narrow in proportionately heavy thickness of walls. The resolution to this was in chamfering the inner edges of sides, sills and in instances lintel heads. This method gave a ‘sense’ of a larger source of illumination. For paintings on both long walls to be visible, the openings had to be on opposite walls. The placement of openings broke the continuity of the story telling board -the murals.

The basilica of Sant’Apollinare Nuovo in Ravenna –For wall art to be seen Windows on opposite face are necessary

Glass had its own tinge of colour which affected the colour scheme of the wall art. One way of diluting the tinge effect was to produce glass as thin as possible. This was done by blowing glass cylinders or bulbs and flattening them. This glass had imperfections that marred the visual clarity. The blown glass panes when placed in lower sections of the building distorted the scenery. Some form of occluding was required. Dwellings began to have sheer curtain masking, and in religious stained and painted glasses were used.

A surface, is often the reason, why an object is being preferred or rejected for a use, and continues to survive in a particular setting. A user perceives the surface of a material-object in many different conditions. A surface is the most proximate and tangible part of an object. The proximity to a surface defines its visual experience whereas the tangibility refers to the mainly tactile sensorial characteristics. Texture is an important qualitative parameter of a surface definition. Textures are intimately linked to specific objects, and deviation from that is immediately registered.

Texture by Modification

Textures are part of naturally occurring objects. We also fashion new finishes by varying the textural qualities. An object acquires a specific colour ‘tinge’ as the texture affects the angle of reflection of light. The angle of perception also has similar effect. The quality of light (the spectral range) and its brightness affect the perception of texture.

‘There are more than 20 mathematical parameters applied to surface description, and some of the terms are: roughness, irregular features of wave, height, width, lay, and direction on the surface; camber, deviation from straightness; out of flat, measure of macroscopic deviations from flatness of a surface.’

We perceive textures through Two basic manners. Visual textures occur through variations in grades of monochrome or coloured surfaces, aided by the shape, size, direction of objects. Contour variations cause tactile textures. But without going closer to the object we perceive the textures through play of shadows and illumination. At this remote perception the texture is visual happening.

Surface texture is a roughness that can be quantified by the vertical deviations from its “ideal form”. Surface roughness is a very subjective term what is rough for some context may be perceived to be smoother for other conditions. Surface textures are perceived for their extent. Surface texture is also sensed in terms of its proximity as well as its tangibility. A brick wall may be very rough to touch but a very extensive surface may not be perceived to be so rough.

Textured surfaces have larger area, so greater reactivity with the environment. Roughness of the surfaces and have higher friction coefficient so susceptible higher wear. Surface irregularities are nucleation nodes for trapping of moisture and promote corrosion. Surface texture allows better adhesion.

In the past half a century, cement has come to predominate all the architectural surface finishes. Cements are Portland and to a limited extent Alumina cements, with many additives and fillers. Some additives and fillers contribute positively to improve the qualitative aspects such as strength, water proofing, homogeneity, shrinkage, rapid or low setting. While others are used to increase the bulk, to reduce cost with or without affecting the quality. Sand, lime, plaster of Paris, stone aggregates, cinders, expanded aggregates like vermiculite, fly ash, pozzolana, surkhi, gravel, metal turnings, asbestos, fiber-glass etc. and chemicals like metal stearates, silicates, polymers aluminium powder pastes etc. are used as additives and fillers.

Cement + water pastes have a tendency, for flocculation and form minute air bubbles an emulsion like mass, and tendency to set falsely. The paste as result has very poor workability and is good for very thin float type applications.

Cement + sand mixtures overcome the flocculation, emulsion like mass forming and false setting problems, and yet provide a reasonable workability. Addition of lime or proprietary chemicals improves the workability, but slows down the setting of cement. Plaster of Paris due to its affinity to water helps in through wetting,improve rendering of cement, but with increased time for setting.

Asbestos, glass fibres etc. reinforce the inter-particle bondage, i.e., homogenize the cement finish. Chemical like aluminium powder or flakes react with silicates of cement to form a foamy air-entrained paste, which on setting and drying retains sufficient spongy mass to insulate the base. Sodium silicate, sodium carbonate and certain sulphate form the basis of proprietary water proofing compounds.

PROBLEMS WITH CEMENT FINISHES

Cement finishes whether smooth or textured, new or old, pose some of these problems:

● fine hair cracks

● honey comb voids

● unbounded loose particles

● foreign particles stuck on the surface

● foreign particles deposited on the surface.

● washable salts leached out from the surface

● salts and compounds formed over the surface by the constituents of the environment

● mould and fungi type bacterial growth

● disengagement from the substrate -peel off.

Cracks appear in both thick and thin masses of cement finishes. Very quick drying and sucking up of moisture by the thirsty substrate, the water needed for complete reaction, cause fine cracks. Saturated substrates often release excess moisture due to temperature change, and this disturbs the bonding to substrates. Unevenly bonded mass soon splits up. Unsound impurities like magnesium salts cause expansion and crack the surface. Where thick finishes are required multi coat application system, allow each coat to readjust the shrinkage stresses and thus reduce cracking. Where thin coats are unavoidable, the surface should be textured so that hair cracks are not easily visible.

Honey comb voids usually occur due to improper mixing and over stirring of ingredients. Method of application (pouring, placement, vibration, compaction) can overcome the air entrained voids, Trowel or float pressure on the surface can squeeze out excess water and consolidate the mass. Pressure spraying and guniting give a well-compacted mass. The voids, not only increase the total area of atmospheric exposure but also the moisture retention capacity of the surface. Consequently leaching of salts, decomposition of surface ingredients, bacterial growth increases.

Ingredients of cement surface finish remain loose or unbounded due to, lack of sufficient binder, poor wettability of fillers, flocculation due to very fine size of particles, oversized particles in terms of surface finish thickness and due to inadequate trowelling pressure. Loose particles get off the surface when fricative forces become operative. This may not damage the surface, but does contaminate the surroundings (e.g. drug or micro electronic plants). Beside the obvious remedies such as use of leaner mix (high wet plasticity), use of wetting agents, proper mixing, judicious selection of particle sizes and proper trowelling, air blasting and pressure cleaning can remove the unbounded particles from the cement surface.

If proper protection is not provided during hardening and setting periods, foreign or redundant particles such as, aggregates, sand, wood chips, saw dust, metal turnings get stuck up on the cement surface. Many of these materials, though, are inert and removable, but do dent the surface.

Moisture reacts with or dissolves the soluble ingredients, the compounds formed after setting and other deposited impurities. Resultant softened, dissolved and loosened substances get carried over to the micro cavities of the surface, where they dry out and remain till mechanically removed, blown off by air or washed away by water shower. However, in the intervening period some of these substances react with atmospheric carbon dioxide, sulphur dioxide, air borne bacteria and fungi, sea salts etc. to form newer substances. Which if insoluble and harmful may have to be removed by rubbing, sanding or treating with suitable chemicals. Cement finish compounds are usually alkaline, so can be neutralized with mild acids, and then dislodged by plain water washing.

Louis Kahn Parliament Concrete Building BanglaDesh

Voids, dents, downs of a rough surface are full of moisture and provide an excellent culture for growth or mould, fungi etc. The bacteria are capable of laying latent for months and then revive with the monsoon. The only possible way to eliminate permanently this menace is to make the surface smooth and impervious. Where this is not achievable, periodic treatment of mouldicide and fungicide can help.